The present invention relates to a projection-type image display apparatus for projecting an image on a screen with using an image display element, such as, a liquid crystal panel, etc., and in particular, it relates to a technology of improving an installation (i.e., a degree of freedom of installation) of that apparatus.
Various kinds of projection-type image display apparatuses are already known and are applied into various fields of applications, widely, for projecting modulated lights, which are obtained by irradiating lights from a light source upon an image display element, on a display portion, such as, a screen or the like, for example, through so-called an enlarging projection optic system, including a projection lens, etc., while displaying an image on that image display element, such as, a transmission-type liquid crystal panel, etc.
Such projection-type image display apparatuses are used, in general, under the condition that the apparatus is installed in the vicinity of the screen or the like. For that reason, to such image display apparatuses, it is requested to shorten that projection distance, while obtaining an enlarged image having a sufficient largeness on the screen at the same time. One of means for achieving this is a wide-angle of the projection lens, and as other means, there are already known an oblique projection method of using a projection lens, having a structure for projecting the image, enlargedly, in a direction inclined to the screen. However, in particular, the oblique projection method of the latter is already disclosed in the following Patent Documents 1 and 2, which will be mentioned below.    [Patent Document 1] Japanese Patent Laying-Open No. Hei 4-27912 (1992); and    [Patent Document 2] Japanese Patent Laying-Open No. 2006-154720 (2006).